Device and method for detecting oscillations of a regulated supply signal

ABSTRACT

The present disclosure relates to a detection circuit for detecting oscillations of a regulated supply signal. The detection circuit includes a filter circuit to filter the regulated supply signal in order to obtain a filtered supply signal. A peak value detector circuit is designed to detect an extremum of the filtered supply signal. A comparator circuit is designed to compare the detected extreme value with a threshold value and to indicate an understepping or exceedance of the threshold value.

RELATED APPLICATION

This application claims priority to German Patent App. No.102020116723.7, filed on Jun. 25, 2020, which is incorporated herein byreference in its entirety.

FIELD

The present disclosure relates to devices and methods for detectingoscillations of a regulated supply signal, such as, for example, fordetecting oscillations of a regulated supply voltage.

BACKGROUND

In voltage regulators designed as an integrated circuit, stability of acontrol loop can be guaranteed, for example, by means of a compensationcapacitor which is connected externally to the integrated circuit (IC).Instability of the regulator can occur, for example, due to a brokenbonding wire or a missing/deactivated external compensation capacitor.The instability of the regulator can result in unwanted oscillations ofa regulated supply signal, such as, for example, a regulated DC voltage.

Such oscillations of regulated DC supply signals (DC=direct current) canbe detected, for example, by means of voltage detectors with comparatorson supply lines. However, this is not readily effective in detectingoscillations at high frequencies (e.g. >10 MHz). Very fast comparatorswould be required for this purpose. The oscillation detection circuitdescribed in U.S. Pat. No. 3,769,596A operates only in a predeterminedfrequency band.

A need therefore exists for improved concepts for detection circuits fordetecting oscillations of a regulated supply voltage, particularly interms of a detection bandwidth.

SUMMARY

This need is taken into account by devices and methods according to theindependent claims Advantageous developments form the subject-matter ofthe dependent claims.

According to a first aspect of the present disclosure, a detectioncircuit is proposed for detecting oscillations of a regulated supplysignal. The detection circuit includes a filter circuit to filter thecontrolled supply signal in order to obtain a filtered supply signal.The detection circuit further includes a peak value detector circuitwhich is designed to detect an extreme value of the filtered supplysignal. The detection circuit further includes a comparator circuitwhich is designed to compare the detected extreme value with a thresholdvalue and to indicate an understepping or exceedance of the thresholdvalue.

Oscillations having a high frequency and/or bandwidth can be detectedthrough the use of peak value detectors. According to exampleembodiments, no fast comparators are required. A maximum oscillationfrequency can be defined by a bandwidth of a peak value detector.According to some example embodiments, a bandwidth of a peak valuedetector of the peak value detector circuit is greater than twice anupper limit frequency for detecting the amplitude fluctuation. A peakvalue detector generally designates a circuit for measuring a maximumvalue of a time-variable signal which, in the simplest design, consistsof a diode and a storage capacitor. The forward voltage of the diode canbe reduced with an operational amplifier in which the diode isincorporated into the negative feedback branch. In addition, a highinput resistance is produced by the operational amplifier. A parallelresistance to the capacitor allows peak values to be registeredcontinuously. A relaxation time and therefore the bandwidth of the peakvalue detector (which defines the minimum oscillation frequency) can beadjusted by means of a discharge time constant of the peak valuedetector.

According to some example embodiments, the regulated supply signal is aregulated DC supply signal (DC=direct current), such as, for example, aregulated DC voltage or a regulated DC current.

According to some example embodiments, the filter circuit includes ahigh-pass or bandpass filter circuit. DC components of the regulatedsupply signal can thus be filtered out and instead only higher-frequency(unwanted) oscillations of the regulated supply signal can be allowed topass through. A lower limit frequency of the filter circuit can depend,for example, on the expected oscillations of the regulated supplysignal.

According to some example embodiments, the detection circuit furtherincludes a reference signal source for setting at least one thresholdvalue signal according to the threshold value for the comparatorcircuit. The reference signal source can include, for example, a bandgapreference circuit. A bandgap reference is a reference voltage sourcewhose output voltage (in a temperature-compensated state) corresponds tothe bandgap voltage of a semiconductor. The generated voltage thusvaries according to the semiconductor material. One particularcharacteristic of a bandgap reference is high precision without complexcircuitry. Detection levels (e.g. oscillation amplitude) can thus beadjusted by means of a DC level, of the threshold value signal.

According to some example embodiments, the peak value detector circuitincludes a first peak value detector for detecting a maximum of the(high-pass-) filtered supply signal and a second peak value detector fordetecting a minimum of the (high-pass-) filtered supply signal. Thecomparator circuit includes a first comparator for comparing thedetected maximum (peak value) with an upper threshold value and a secondcomparator for comparing the detected minimum (peak value) with a lowerthreshold value. However, fast comparators are not required for thispurpose.

According to some example embodiments, the reference voltage source isdesigned to provide a first threshold value signal corresponding to theupper threshold value for the first comparator and a second thresholdvalue signal corresponding to the lower threshold value for the secondcomparator. This can be achieved, for example, by corresponding voltagedividers.

According to some example embodiments, the comparator circuit isdesigned to indicate an amplitude fluctuation of the regulated supplysignal if the detected maximum exceeds the upper threshold value and thedetected minimum understeps the lower threshold value. The circuit canthus be made robust in terms of undershooting or overshooting due toload changes.

According to some example embodiments, the detection circuit is designedas an integrated detection circuit. The integrated detection circuit canbe integrated together with a radar or lidar (light detection andranging) circuit on a common semiconductor chip, and the regulatedsupply signal can be a regulated supply voltage for the radar or lidartransceiver circuit. In one embodiment, the IC can detect oscillationson all supply domains in the frequency range from, for example, 10 kHzto 25 MHz which exceed the respective nominal voltage ranges by, forexample, +/−20%. For highly safety-relevant applications, such as, forexample, radar or lidar applications in connection with autonomousdriving, this can result in the detection of errors and therefore inmore safety.

According to a further aspect of the present disclosure, an integratedcircuit is therefore also proposed, including an integrated radar orlidar circuit, an integrated voltage regulator circuit for providing aregulated supply voltage for the radar or lidar transceiver circuit, andan integrated detection circuit for detecting oscillations of theregulated supply voltage according to one of the preceding exampleembodiments.

According to another further aspect of the present disclosure, a methodis proposed for detecting oscillations of a regulated supply signal,including filtering the regulated supply signal in order to obtain afiltered supply signal, detecting an extreme value of the filteredsupply signal by means of a peak value detector circuit, comparing thedetected extreme value with a threshold value, and indicating anunderstepping or exceeding of the threshold value.

With example embodiments of the proposed detection circuit, a highbandwidth of the oscillations can be detected (e.g. 10 kHz to 100 MHz).No fast comparators are required (the maximum frequency is defined bythe bandwidth of the peak value detector). The detection levels(oscillation amplitude) can easily be adjusted by means of the DC levelof the limit values. The relaxation time of the peak value detector(which defines the minimum oscillation frequency) can easily be adjustedby means of the discharge time constant of the peak value detector. Thedetection circuit can further be designed as insensitive toundershooting or overshooting due to the load changes.

BRIEF DESCRIPTION OF THE DRAWINGS

Some examples of devices and methods are explained in detail belowpurely by way of example with reference to the attached figures. In thefigures:

FIGS. 1A and 1B show an active principle of a detection circuit fordetecting oscillations of a regulated supply signal according to thepresent disclosure;

FIG. 2 shows a block diagram of a detection circuit for detectingoscillations of a regulated supply signal according to the presentdisclosure;

FIGS. 3A and 3B show a schematic block diagram of a detection circuitaccording to one example embodiment;

FIG. 4 shows different interferences of a regulated supply signal andresponses of the detection circuit thereto; and

FIG. 5 shows a flow diagram of a method for detecting oscillations of aregulated supply signal according to the present disclosure.

DETAILED DESCRIPTION

Some examples will now be described in detail with reference to theattached figures. However, further possible examples are not restrictedto the features of these embodiments described in detail. Said furtherpossible examples can have modifications of the features and equivalentsand alternatives to the features. The terminology used herein todescribe specific examples is furthermore not intended to be limitingfor further possible examples.

In the entire description of the figures, identical or similar referencenumbers relate to identical or similar elements or features which can beimplemented in each case in an identical or modified form whileproviding an identical or similar function. The sizes of lines, layersand/or areas can further be exaggerated in the figures for illustrativepurposes.

If two elements A and B are combined using the term “or”, this is to beunderstood to mean that all possible combinations are disclosed, i.e. Aonly, B only, and also A and B, unless expressly defined otherwise inthe individual case. The terms “at least one of A and B” or “A and/or B”can be used as an alternative wording for the same combinations. Thesame applies accordingly to combinations of more than two elements.

If a singular form, e.g. “a, one” and “the” is used and the use of onlya single element is neither explicitly nor implicitly defined asobligatory, further examples can also use a plurality of elements inorder to implement the same function. If a function is described belowas being implemented using a plurality of elements, further examples canimplement the same function using a single element or a singleprocessing entity. It furthermore goes without saying that the terms“comprises”, “comprising”, “has” and/or “having” are used to describethe presence of the indicated features, integers, steps, operations,processes, elements, components and/or a group thereof, but do notexclude the presence or the addition of one or more of the features,integers, steps, operations, processes, elements, components and/or agroup thereof.

FIGS. 1A and 1B show the active principle of a detection circuit fordetecting oscillations of a regulated supply signal according to thepresent disclosure. The waveforms shown in FIGS. 1A and 1B are conjoinedat their respective dotted boundaries to form continuous waveformsacross the figures.

Reference number 110 denotes an oscillating supply signal. The supplysignal 110 may, for example, be a regulated DC voltage signal withoscillations due to voltage regulator instabilities. The regulated DCvoltage signal fluctuates in an unwanted manner, such as, for example,due to a defect (e.g. broken bonding wire), around a DC mean value. FIG.1 shows, purely by way of example, an oscillation at a frequency of 5MHz. An amplitude of the (unwanted) oscillation increases over time. Thesupply signal may, for example, be a voltage supply signal for asemiconductor chip.

It may then be desirable to detect such unwanted oscillations ofregulated supply signals as from a specific oscillation amplitude andthen, if necessary, take measures, such as, for example, an errormessage or a shutdown. FIGS. 1A and 1B shows an upper limit value 120-1and a lower limit value 120-2. The two limit values 120-1 and 120-2 canbe disposed, for example, symmetrically around a mean value of theoscillating supply signal 110. Due to the emergence of the unwantedoscillation of the supply signal 110, the signal amplitude of the lattereventually reaches a level such that the oscillating supply signal 110understeps or exceeds both the upper and the lower limit value 120-1 and120-2. Reference number 130-1 indicates that the upper limit value 120-1has been exceeded. Similarly, the understepping of the lower limit value120-2 is indicated by reference number 130-2. Due to the relatively highoscillation frequency of, here, by way of example, 5 MHz, the exceedance130-1 and the understepping 130-2 take place more or lesssimultaneously. The time at which the limit values 130-1 and 130-2 areexceeded or understepped is indicated in FIG. 1 by reference number 140.At the time 140, two detection signals 50-1 and 150-2 jump from “low” to“high”. The detection signal 150-1 is assigned to the exceedance of theupper limit value 120-1, the detection signal 105-2 is assigned to theunderstepping of the lower limit value 120-2, and, as long as theoscillating supply signal 110 moves within the two limit values 120-1and 120-2, both detection signals 150-1 and 150-2 are in each case“low”. If the oscillating supply signal 110 leaves the range within thelimit values 120-1 and 120-2, the detection signals 150-1 and 105-2 ineach case jump to “high”.

The supply voltage 110 to be monitored can, for example, behigh-pass-filtered. Two peak value detectors, for example, can track theupper and lower peaks of the filtered supply voltage at the output of ahigh-pass filter. The peak levels can be compared with an upper and alower limit value 120-1, 120-2. If the peak levels exceed both the upperand the lower limit value 120-1, 120-2, a supply oscillation can bedetected.

A schematic block diagram of a detection circuit 200 with whichoscillation amplitudes of a regulated supply signal above specific limitvalues can be detected, is shown schematically in FIG. 2 .

The detection circuit 200 comprises a filter circuit 210 to filter theregulated (and unwantedly oscillating) supply signal 110 in order toobtain a filtered supply signal 212. The filter signal 210 may, forexample, be a bandpass filter circuit or a high-pass filter circuit. Thedetection circuit 200 further comprises a peak value detector circuit220 which is designed to detect an extreme value (minimum and/ormaximum) of the filtered supply signal 212. The detection circuit 200further comprises a comparator circuit 230 which is designed to comparethe detected extreme value 222 with a predefined limit value orthreshold value 232 and to indicate an exceeding or understepping of thethreshold value at its output 234.

The block diagram shown in FIG. 2 presents only a schematic view inorder to illustrate the underlying principles of the present disclosure.The individual blocks 210, 220, 230 can be implemented in numerousdifferent ways by means of circuitry. One possible implementation isexplained in detail below with reference to FIGS. 3A and 3B. FIGS. 3Aand 3B are conjoined at their respective dotted boundaries to form asingle schematic block diagram.

The detection circuit 300 shown in FIGS. 3A and 3B for detectingoscillations of a regulated supply signal comprises an input 301 for theregulated supply signal 110. On the input side, the detection circuit300 comprises a high-pass filter circuit which comprises a capacitor 302and a resistor 304. On the output side, a peak value detection circuit220 is connected to the high-pass filter circuit. The peak valuedetector circuit 220 comprises a first peak value detector 220-hi and asecond peak value detector 220-low. On the output side, the peak valuedetector circuit 220 is connected to a comparator circuit 230. Thecomparator circuit 230 comprises a first comparator 230-hi connected tothe output of the first peak value detector 220-hi, and a secondcomparator 230-low connected to the output of the second peak valuedetector 220-low. Limit value exceedances of the oscillating supplysignal 110 can be indicated with corresponding detection signals at theoutputs of the comparators 230-hi and 230-low. The outputs of thecomparators 230-hi and 230-low are logically linked via an AND gate 336.An oscillation of the regulated supply signal can be indicated at theoutput of the AND gate 336.

An input connection 301 of the detection circuit 300 can be connected,for example, to a voltage regulator which normally provides a regulatedDC voltage. Under certain circumstances, this can result in theoccurrence of unwanted oscillations of the regulated DC voltage. Theseoscillations or exceedances of oscillation amplitudes in relation tospecific limit values can be identified with the detection circuit 300.In order to filter out DC components of the oscillating supply signal110, the input 301 of the detection circuit 300 is connected in theexample embodiment shown in FIGS. 3A and 3B to a high-pass filtercomprising the capacitor 302 and the resistor 304. A bandpass filtercircuit could also be provided as an alternative to the high-pass filtercircuit.

The input connection 301 of the detection circuit 300 is connected to afirst electrode of the capacitor 302. A second electrode of thecapacitor 302 is connected to a first connection of the resistor 304. Asecond connection of the resistor 304 is connected to ground. Thehigh-pass-filtered supply signal 212 can be tapped at a node “vcmp”between the capacitor 302 and the resistor 304. The node “vcmp” isconnected to both an input of the first peak value detector 220-hi andan input of the second peak value detector to 220-low. The first peakvalue detector to 220-hi serves to detect upper peak values of theoscillating supply signal, while the second peak value detector 220-lowserves to detect lower peak values of the oscillating supply signal. Thedetected upper peak value 222-hi is fed to a first input of the firstcomparator 230-hi. A first (upper) threshold value signal 232-hi whichis provided by means of a reference signal source 340 is fed to thesecond input of the first comparator 230-hi. The detected lower peakvalue 222-low is fed to a first input of the second comparator 230-low.A second (lower) threshold value signal 232-low which is similarlyprovided by means of the reference signal source 340 is fed to thesecond input of the second comparator 230-low.

The reference signal source 340 comprises a differential amplifier 341and transistors 342, 343, 344 connected in parallel at its outputbetween a supply potential vdd and ground. An output voltage vref of thedifferential amplifier 341 is stabilized at a point where thecharacteristics of the transistors 342, 343, 344 intersect. The gateconnections of the transistors 342, 343, 344 are connected in each caseto the output of the operational amplifier 341. A resistor 347 isconnected between the drain connection of the transistor 342 and ground.Two resistors 345, 346 are connected in series between the drainconnection of the transistor 343 and ground. The first threshold valuesignal 232-hi can be tapped between the drain connection of thetransistor 343 and the resistor 345. The second threshold value signal232-low can be tapped between the two resistors 345 and 346.

In example embodiments, individual circuit blocks can also beimplemented in ways other than those shown.

The supply signal monitored by the detection circuit 300 is thereforehigh-pass-filtered (vcmp). A DC voltage level of the filtered signalvcmp lies between the two limit values 232-hi, 232-low (lim_hi andlim_lo). Two peak value detectors 220-hi, 220-low are connected to thefiltered supply signal vcmp. The output signals 222-hi, 222-low of thepeak value detectors (peak_hi, peak_lo) are compared with the upper andlower limit value 232-hi, 232-low (lim_hi, lim_lo) which can have a DCvoltage difference compared with the DC voltage level of thehigh-pass-filtered supply signal which is adjustable via the resistors345, 346, 347. With a corresponding oscillation at the supply input 301,both output signals 222-hi, 222-low of the peak value detectors 220-hi,220-low exceed their limits. This can be indicated by the outputosc_detect of the AND gate 336.

The DC level difference compared with lim_hi/lo to vcmp can beadjustable. Slow high or low peaks (e.g. caused by load change on theregulator) can be detected as “peak_hi”/“peak_lo”, but not as anoscillation. An upper frequency limit of the detection is provided bythe bandwidth of the peak value detectors 220-hi, 220-low which can bedesigned as very high (e.g. ˜100 MHz or even higher). A lower frequencylimit can be defined by the discharge time of the peak value detectors220-hi, 220-low. With additional logic (e.g. digital counters), evenlower frequencies can be detected if long discharge times are notdesired/possible. These relationships are shown graphically in FIG. 4 .

The detection circuit 200, 300 can be designed, for example, as anintegrated circuit and can be integrated together with an integratedradar or lidar circuit on a common semiconductor chip. The regulatedsupply signal 110 can be a regulated supply voltage for the integratedradar or lidar circuit and can be provided by an integrated voltageregulator.

To summarize, FIG. 5 also shows a flow diagram of a method 500 fordetecting oscillations of a regulated supply signal.

The method 500 comprises filtering 510 the regulated supply signal inorder to obtain a filtered supply signal, detecting 520 an extreme valueof the filtered supply signal by means of a peak value detector circuit,comparing 530 the detected extreme value with a threshold value, andindicating 540 an understepping or exceedance of the threshold value.

The aspects and features which are described in connection with onespecific example of the preceding examples can also be combined with oneor more of the further examples in order to replace an identical orsimilar feature of this further example or additionally to introduce thefeature into the further example.

Examples can furthermore be or relate to a (computer) program with aprogram code to carry out one or more of the above methods if theprogram is executed on a computer, a processor or a differentprogrammable hardware component. Steps, operations or processes ofvarious of the methods described above can therefore also be performedby programmed computers, processes or other programmable hardwarecomponents. Examples can also cover program memory devices, e.g. digitaldata storage media, which are machine-readable, processor-readable orcomputer-readable, and which code or contain machine-executable,processor-executable or computer-executable programs and instructions.The program memory devices can be or comprise e.g. digital memories,magnetic storage media, such as, for example, magnetic disks andmagnetic tapes, hard drives or optically readable digital data storagemedia. Further examples can also cover (field) programmable logic arrays((F)PLAs), (field) programmable gate arrays ((F)PGAs), graphicsprocessor units (GPUs), application-specific integrated circuits(ASICs), integrated circuits (ICs) or a system-on-a-chip (SoC) which areprogrammed to carry out the steps of the methods described above.

It furthermore goes without saying that the disclosure of a plurality ofsteps, processes, operations or functions disclosed in the descriptionor the claims is not intended to be understood to mean that theyinvariably take place in the described sequence, unless this isexplicitly indicated in individual cases or is absolutely essential fortechnical reasons. The performance of a plurality of steps or functionsis not therefore limited by the preceding description to a specificsequence. Moreover, in further examples, a single step, a singlefunction, a single process or a single operation can include and/or canbe subdivided into a plurality of substeps, subfunctions, subprocessesor suboperations.

If some aspects in the preceding sections have been described inconnection with a device or a system, these aspects are also to beunderstood as a description of the corresponding method. Thus, forexample, a block, device or functional aspect of the device or of thesystem can correspond to a feature, such as a method step, of thecorresponding method. Correspondingly, aspects which are described inconnection with a method are also to be understood as a description of acorresponding block, a corresponding element, a characteristic or afunctional feature of a corresponding device or of a correspondingsystem.

The following claims are incorporated herewith into the detaileddescription, wherein each claim can stand alone as a separate example.It should also be noted that—although a dependent claim relates in theclaims to a specific combination with one or more other claims—otherexamples can also comprise a combination of the dependent claim with thesubject-matter of every other dependent or independent claim. Suchcombinations are herewith explicitly proposed, unless it is indicated inindividual cases that a specific combination is not intended.Furthermore, features of a claim are intended to be included in eachother independent claim, even if this claim is not directly defined asdependent on this other independent claim.

What is claimed is:
 1. A detection circuit for detecting oscillations ofa regulated supply signal, the detection circuit comprising: a filtercircuit configured to filter the regulated supply signal in order toobtain a filtered supply signal; a peak value detector circuitconfigured to detect an extreme value of the filtered supply signal; anda comparator circuit configured to compare the detected extreme valuewith a threshold value and to indicate at least one of an understeppingor exceedance of the threshold value.
 2. The detection circuit asclaimed in claim 1, wherein the filter circuit comprises a high-passfilter or a bandpass filter.
 3. The detection circuit as claimed inclaim 1, further comprising: a reference signal source configured toadjust at least one threshold value signal according to the thresholdvalue for the comparator circuit.
 4. The detection circuit as claimed inclaim 3, wherein the reference signal source comprises a bandgapreference circuit.
 5. The detection circuit as claimed in claim 1,wherein: the peak value detector circuit comprises a first peak valuedetector configured to detect a maximum of the filtered supply signal,and a second peak value detector configured to detect a minimum of thefiltered supply signal, and wherein: the comparator circuit comprises afirst comparator configured to compare the detected maximum with anupper threshold value, and a second comparator configured to compare thedetected minimum with a lower threshold value.
 6. The detection circuitas claimed in claim 5, wherein a reference voltage source is configuredto provide a first threshold value signal corresponding to the upperthreshold value for the first comparator, and provide a second thresholdvalue signal corresponding to the lower threshold value for the secondcomparator.
 7. The detection circuit as claimed in claim 5, wherein thecomparator circuit is configured to indicate an amplitude fluctuation ofthe regulated supply signal if the detected maximum exceeds the upperthreshold value and the detected minimum understeps the lower thresholdvalue.
 8. The detection circuit as claimed in claim 7, wherein abandwidth of the first peak value detector and a bandwidth of the secondpeak value detector are greater than twice an upper limit frequency fordetecting the amplitude fluctuation.
 9. The detection circuit as claimedin claim 1, wherein the detection circuit is configured as an integrateddetection circuit.
 10. The detection circuit as claimed in claim 9,wherein the integrated detection circuit is integrated together with aradar circuit or a lidar circuit on a common semiconductor chip, and theregulated supply signal is a regulated supply voltage for the radarcircuit or the lidar circuit.
 11. An integrated circuit, comprising: anintegrated radar circuit or an integrated lidar circuit; an integratedvoltage regulator circuit configured to provide a regulated supplyvoltage for the integrated radar circuit or the integrated lidarcircuit; and an integrated detection circuit configured to detectoscillations of the regulated supply voltage, the integrated detectioncircuit comprising: a filter circuit configured to filter a regulatedsupply signal corresponding to the regulated supply voltage in order toobtain a filtered supply signal; a peak value detector circuitconfigured to detect an extreme value of the filtered supply signal; anda comparator circuit configured to compare the detected extreme valuewith a threshold value and to indicate at least one of an understeppingor exceedance of the threshold value.
 12. A method for detectingoscillations of a regulated supply signal, the method comprising:filtering the regulated supply signal in order to obtain a filteredsupply signal; detecting at least one extreme value of the filteredsupply signal by means of a peak value detector circuit; comparing theat least one extreme value with a corresponding threshold value; andindicating at least one of an exceedance or understepping of thecorresponding threshold value by the at least one extreme value.
 13. Themethod as claimed in claim 12, wherein filtering the regulated supplysignal in order to obtain the filtered supply signal comprises ahigh-pass or a bandpass filtering.
 14. The method as claimed in claim12, wherein the at least one extreme value includes a maximum of thefiltered supply signal that is detected with a first peak value detectorand a minimum of the filtered supply signal is detected with a secondpeak value detector, and wherein comparing the at least one extremevalue with the corresponding threshold value includes comparing themaximum of the filtered supply signal with an upper threshold value andcomparing the minimum of the fitered supply signal with a lowerthreshold value.
 15. The method as claimed in claim 14, whereinindicating the exceedance or understepping of the correspondingthreshold value by the at least one extreme value includes: indicatingan amplitude fluctuation of the regulated supply signal if the maximumof the filtered supply signal exceeds the upper threshold value and theminimum of the filtered supply signal understeps the lower thresholdvalue.